This application claims priority based on Japanese Patent Application No. 11-358780 filed Dec. 17, 1999 and entitled xe2x80x9cGolf Club and Set of Golf Clubs.xe2x80x9d
This invention relates to a golf club that has improved swing characteristics while maintaining the high ball flying distance and to a set of such golf clubs.
A golf club has a head, which strikes balls, a grip, which a golfer holds, and a shaft, which connects the head and the grip. A set of golf clubs generally includes nine or ten xe2x80x9cironxe2x80x9d type clubs and some xe2x80x9cwoodxe2x80x9d type clubs. Each of these clubs has a different club length, loft angle, and a head mass to meet requirements such as a flying distance and strike angle. For example, a wedge club, which is suitable to propel a ball short distances, has a club length of about 0.9 meters and a head mass of about 0.29 kilograms. On the other hand, a driver, which is suitable to propel a ball long distances, has a club length of about 1.14 meters and a head mass of about 0.2 kilograms.
Manufacturers of golf clubs continually improve the design of clubs to produce clubs that are easier to swing and that propel balls over greater distances with less work, regardless of above-mentioned differences in characteristics of each club.
The problem that a club having a longer target flying distance (i.e., a smaller club number) is harder to swing and requires more work has not yet been solved. To obtain a greater flying distance, the head should have a higher speed when the head impacts the ball. One of the effective methods of increasing the head speed is to increase the club length (LC). However, if the club length is longer, the mass of the club increases and the equivalent pendulum length (LPE) around the rotation center (upper end of the grip of the club) increases. This increases the work of swinging the club. That is, to increase the ball flying distance by increasing the club length presents a physical contradiction.
To overcome this contradiction, for example, U.S. Pat. No. 5,467,984 discloses a golf club for which the ratio of the equivalent pendulum length to the club length (LPE/LC) is less than 0.87 when the LPE is measured along the axis from the upper end of the grip to 101.6 mm below the upper end. This patent provides a club that has a total mass of less than 340 g and has improved swing characteristics without changing the club length. This is achieved by reducing the mass of the grip and the shaft and by adding a weight, the mass of which is equal to reduced mass of the grip and the shaft, at the middle of the shaft.
The shorter the equivalent pendulum length of the club is, the easier it is to swing the club. There are two most effective methods to shorten the equivalent pendulum length. One is to shorten the club length. The other is to reduce the mass of the head. Both methods have disadvantages. Shortening the club reduces the head speed and thus reduces the flying distance. The small head mass reduces the rebound ratio of the head against the ball. This also reduces the ball flying distance.
Apart from the prior art described above, to shorten the equivalent pendulum length without changing the club length and the head mass, it is most effective to reduce the grip mass and the shaft mass and add a weight, the mass of which is equal to the sum of the reduced mass, at the middle of the shaft. This improves the xe2x80x9cfeelxe2x80x9d of the club. However, the prior art has not yet revealed whether this design alteration is associated with the flying distance, in other words, the prior art does not explain how the head mass and the shaft mass should be determined relative to the club length to maintain the high flying distance.
A golf club that is easy to swing and provides a greater target flying distance with less work and a set of such golf clubs do not existed.
Accordingly, one object of the present invention is to provide a golf club that has improved swing characteristics while maintaining high flying distance with less work by calculating the optimum mass distribution of the club while keeping the club length constant. Also, another object of the present invention is to provide a set of such golf clubs.
The golf club of the present invention includes a shaft, a head, and a grip. The shaft has a tip end and a butt end. The head is attached to the tip end of the shaft. The grip is attached to the butt end of the shaft. The 14-inch balance of the club is D0 or more. The initial velocity per equivalent pendulum length Vb/Lp larger than xe2x88x923.57 Lc+64.58 Vb is the initial velocity of the ball. Lp is the equivalent pendulum length of the club when an upper end of the grip is taken as a rotation center. Lc is the club length as measured from the upper end of the grip to a perpendicular projection of the center of gravity of the head along the axis of the shaft. The initial velocity of the ball is:
Vb=1.8 Mh(56.22 Lcxe2x88x9235.16 Mcxe2x88x9239.77 Lp+31.61)/(Mh+0.0455).
Mh is the mass of the head (kg) and Mc is the total mass of the club (kg).
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.